REDUNDANT ELECTRIC MOTOR ARRANGEMENT INCLUDING SINGLE ROTOR ASSEMBLY HAVING TWO MAGNET SECTIONS

Abstract: A redundant electrical drive motor has a rotor assembly including a pair of coaxial permanent magnet sections (2, 4) and a pair of stator assemblies (16, 18), one for each of the magnet sections (2, 4). The magnet sections and the stator assemblies are mounted in tandem. The arrangement described minimizes motor size and weight and achieves high reliability and efficiency for applications where a back-up or redundant capability is required.

Description: REDUNDANT ELECTRIC MOTOR ARRANGEMENT INCLUDING SINGLE ROTOR ASSEMBLY HAVING TWO MAGNET SECTIONS CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation-In-Part of commonly assigned co-pending U.S. Application Serial No. 08/167,375 filed on December 14, 1993. BACKGROUND OF THE INVENTION This invention relates to high speed redundant electrical machines used, for example, for driving aircraft vapor cycle compressors. More particularly, this invention relates to an electrical machine for the purpose described which includes a single rotor having two separate identical permanent magnet sections operating in conjunction with two separate identical toroidally wound two pole stator sections. These machines desirably have minimum weight and size, electromagnetic and physical isolation of the two rotor sections, high reactance, low short-circuit current capability for fault tolerance and current wave shape filtering, high reliability and efficiency, and low cost. It will be appreciated that machines of the type described solve a particular drive motor redundancy problem. A non-redundant drive motor having only a single motor section and the same power (HP) and speed (RPM) rating would be simpler in construction and of lower cost and weight, as will be readily understood. Minimum weight and size requirements are compatible with high reactance, low fault current characteristics. The flux utilization factor for a toroidally wound motor versus the conventional type motor inherently results in higher motor reactance (for the same motor flux, approximately twice the number of turns are required for the same voltage) . In case of an internal or external fault, the low internal winding losses due to the low fault current can be removed and dissipated by the motor cooling system. Additionally, the high reactance acts as a filter for the motor input current, therefore 5 benefitting overall system weight and size. High reliability and low cost are achieved simultaneously with simplicity in design and a low parts count, as is high efficiency. The present applicant is aware of the following 10 U.S. patents which relate generally to electric motors of the type described: U.S. Patent 4,625,135 (U.S. Class 310/156) which issued on November 25, 1986 to Kasabian; U.S. patent 4,617,726 (U.S. Class 29/598) which issued on October 21, 1986 to Denk; U.S. Patent 15 4,667,123 (U.S. Class 310/156) which issued on May 19, 1987 to Denk, et al; U.S. Patent 4,709,180 (U.S. Class 310/179) which issued on November 24, 1987 to Denk; U.S. Patent 4,741,094 (U.S. Class 29/598) which issued on May 3, 1988 to Denk, et al; U.S. Patent 4,852,245 20 (U.S. Class 29/596) which issued on August 1, 1989 to Denk; U.S. Patent 4,987,674 (U.S. Class 29/596) which issued on January 29, 1991 to Denk; U.S. Patent 5,030,877 (U.S. Class 290/52) which issued on July 9, 1991 to Denk; and U.S. Patent 5,233,252 (U.S. Class 25 310/254) which issued on August 3, 1993 to Denk. The multi-section rotor shown in Figure 7 of U.S. Patent 4,625,135 features a ferro-magnetic through shaft that provides a return path for four, six and twelve pole sections. 30 This shaft also provides the longitudinal stiffness needed for high speed operation. However, none of the aforementioned patents addresses the redundant feature of the present invention. In this regard, it is noted that the present invention improves on the prior art 35 patents that particularly relate to two pole toothless permanent magnet rotor machines. Accordingly, it is the object of this invention to provide a drive motor of the type described having two identical motor sections and featuring a single rotor assembly having two coaxial cylindrical permanent magnet rotor sections and two stator assemblies corresponding to the permanent magnet sections. Each of the motor sections can be powered from a different electrical bus to achieve redundancy and maximum system reliability. SUMMARY OF THE INVENTION This invention contemplates an electrical drive motor arrangement having a rotor assembly and a stator assembly. The rotor assembly includes a pair of identical coaxial cylindrical two pole permanent magnet sections, a pair of non-magnetic stub shafts, a non¬ magnetic magnet separator and a non-magnetic retaining hoop. The retaining hoop has sufficient diametral interference with the permanent magnet sections, the stub shafts and the separator to insure that the sections are held together with the respective stub shafts and non-magnetic magnet separator in compression over desired operating speed and temperature conditions. The stator assembly includes a pair of stators, one for each of the permanent magnet sections. The magnet sections and the respective stator assemblies are arranged in tandem to achieve desired redundancy. Typically, for a three phase motor, each stator assembly has six individually toroidally-wound sixty degree half-phase sectors. It will be appreciated that the use of toroidally wound stators for high speed redundant motors will result in minimum end turn extension length. This allows the rotor sections to be used for high speed applications without excessive rotor length, and eliminates shaft critical speed problems. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially sectioned diagrammatic elevational view illustrating the invention. Figure 2 is a diametral cross-sectional representation of a stator assembly according to the invention. Figure 3 is an enlarged portion of Figure 2 particularly illustrating the structural details of the stator assembly. Figure 4 is a partial longitudinal sectional representation of the stator assembly. DETAILED DESCRIPTION OF THE INVENTION With reference to the several Figures in the drawing, wherein corresponding components carry corresponding numerical designations, a drive motor is designated by the numeral 1. Motor 1 is of the two-pole, three-phase, toothless toroidal winding type. Only as much of motor 1 as is necessary to understand the invention will be herein illustrated and described. Motor 1 includes a rotor assembly including a pair of coaxial cylindrical two-pole permanent magnet sections designated by the numerals 2 and 4. Magnet sections 2 and 4 are surrounded by a pair of non¬ magnetic stub shafts 8 and 10, respectively, and supported by a non-magnetic retaining hoop 6. A non¬ magnetic separator 12 separates magnet sections 2 and 4. Non-magnetic retaining hoop 6 has sufficient diametral interference with the assembly including magnet sections 2 and 4, stub shafts 8 and 10 and separator 12 to insure that the assembly is compressively retained over the operating speed and temperature range of motor 1. A bore seal tube 7 is part of an assembly along with a retainer 14 which retains a pair of stator assemblies 16 and 18 in operative relation with magnet sections 2 and 4, respectively. Each of the stator assemblies 16 and 18 has a laminated flux collector ring such as 20 which is surrounded by insulation such as 21 and the toroidal windings. A winding barrier 22 having a plurality of through holes for cooling flow separates the respective stator assemblies 16 and 18. With the arrangement described magnet sections 2 and 4 and respective stator assemblies 16 and 18 are arranged in tandem, as will now be discerned. The windings such as 24 of stators 16 and 18 are of Litz cable (fine stranded, fully transposed conductors) which controls eddy current losses, eliminate circulating current losses in the copper strands of the windings, and provides a large effective surface area for cooling as is desireable. As particularly illustrated in Figure 2, each of the stator assemblies 16 and 18 (stator assembly 16 shown for illustration purposes) includes six individually toroidal-wound unvarnished or fully encapsulated sixty degree half-phase sectors, i.e. dedicated phase sectors A, B and C half phase coils and half phases A' , B ! and C . Adjacent phases are separated by phase-to-phase insulators/separators designated by the numeral 25. Retainer 14 surrounds the windings of the stator assemblies. With particular reference to Figure 3, insulator/separators 25 are keyed into retainer 14 and bore seal tube 7, and a rotating clearance CL is provided between the rotor and stator assemblies. With particular reference to Figure 4, a motor housing is designated by the numeral 30. A stator retaining ring 32 is secured to frame 14 and housing 30 via a fastening means such as a screw or the like 34. Flow-through cooling on the outer surfaces of fully encapsulated windings is as indicated by the arrows in Figure 1. For unvarnished windings coolant flows through the Litz conductors in addition to said outer surfaces. It will be appreciated that conventional stator windings using slotted configurations have two coil sides per slot of different phase windings. Full phase-to-phase voltage potential exists between these coil sides as well as between phase windings, which cross over each other in the end turns, thus limiting stator robustness and reducing viability. The configuration of the present invention as shown and described avoids this disadvantage as will now be discerned. It will be understood that individual toroidal wound dedicated half-phase sector segments, as particularly shown in Figure 2, provide the best achievable winding protection against phase-to-phase and winding ground shorts. Winding reliability and fault tolerance are accordingly much higher than achieved by other stator configurations. There has thus been described a motor arrangement which satisfies the aforementioned object of the invention by featuring a single rotor assembly including a pair of coaxial permanent magnet rotor sections. The permanent magnet rotor sections and two corresponding stator assemblies are tandem mounted. A protective winding barrier is installed between the two stator assemblies and a non-magnetic separator separates the magnet sections. With the above description of the invention in mind, reference is made to the claims appended hereto for a definition of the scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A redundant electric motor arrangement, comprising: a bore seal tube; a single rotor assembly including a pair of identical coaxial cylindrical two pole permanent magnet sections disposed within the bore seal tube; a non-magnetic retaining hoop disposed within the bore seal tube; a pair of non-magnetic stub shafts disposed within the bore seal tube and supported by the non-magnetic retaining hoop, each of said non-magnetic stub shafts disposed on one end of a corresponding permanent magnet section of the pair of said sections; a non-magnetic separator disposed within the bore seal tube for axially spacing and locating the pair of permanent magnet sections; the non-magnetic retaining hoop surrounding and retaining the permanent magnet sections, the stub shafts and the non-magnetic separator; a pair of stator assemblies, each of which is disposed outside the bore seal tube in operative relation with a corresponding magnet section of the pair of said sections; a retainer surrounding the pair of stator assemblies; and said retainer and said bore seal tube cooperating to retain the pair of stator assemblies in operative relation with the corresponding magnet sections of said single rotor assembly, with said magnet sections and said corresponding stator assemblies being thereby retained in tandem to provide the redundant electric motor arrangement. 2. The arrangement as described by claim 1, wherein: the non-magnetic retaining hoop has sufficient interference with the pair of permanent magnet sections, the respective stub shafts and the non-magnet separator to insure that said sections, stub shafts and retainer are retained in compression over desired motor operating speed and temperature conditions. 3. The arrangement as described by claim ____. , wherein each of the pair of stator assemblies includes: six individually toroidally-wound sixty degree half-phase sectors. 4. The arrangement as described by claim 3, including: insulator/separators for separating adjacent phases of the six individually toroidally wound sixty degree half-phase sectors. 5. The arrangement as described by claim 4, wherein: the insulator/separators are keyed into the retainer and the bore seal tube. 6. The arrangement as described by claim l, including: a motor housing; a stator assembly retaining ring; and means for securing the stator retaining ring and the retainer to the motor housing. 7. The arrangement as described by claim 3, wherein: each of the stator assemblies includes a flux collector ring surrounded by insulation means and the toroidal stator windings. 8. The arrangement as described by claim l, including: a barrier for separating respective windings of the pair of stator assemblies.

Inventors: DENK JOSEPH, DENK, JOSEPH
Applicants: ALLIED SIGNAL INC, ALLIEDSIGNAL INC.
Application year: 1994
Main classification: H02K16
IPC codes: H02K1, H02K3, H02K16, H02K21